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Mr. E. G. Young. 



precipitated by small quantities of electrolytes. Michaelis endorsed this view 

 from his work on serum albumin. Most workers have confined themselves to 

 a study of the conditions governing flocculation, and the more fundamental 

 primary change from a natural protein to one which is readily precipitated on 

 neutralisation of the charge carried by the particles has been neglected. 



The explanation of coagulation generally accepted is due to Hofmeister and 

 Panli. They conceive of the primary change as one of dehydration involving 

 the internal neutralisation through the loss of the elements of water of 

 terminal NH2 and COOH groupings. From a study of the coagulation of 

 casein by alcohol Eobertson comes to the same conclusion. 



Now in the change brought about by sunlight there are two reactions. The 

 first change involves a simple chemical one, for which the light is responsible, 

 which causes an increase in optical rotatory power and in viscosity, a decrease 

 in surface tension and a decrease in H or OH ions depending on the reaction 

 of the medium. The second stage will only precede if the solution is at or 

 near the isoelectric point. It is materially aided by small amounts of electro- 

 lytes or dehydrating agents such as alcohol or acetone. Under certain 

 circumstances the second stage is reversible. The explanation would seem to 

 lie in the ability of the albumin to reassume charged ions so long as agglutina- 

 tion has not proceeded too far. In other words the forces of repulsion of 

 similarly charged ions attached to the colloidal particles are sufficient to 

 overcome the adhesive forces of the albumin flocculi. It is conceivable that 

 in the primary stage not only do we have internal anhydride formation within 

 single colloidal aggregates, but that as coagulation proceeds this anhydride 

 formation extends to linkages between two or more colloidal aggregates. The 

 determination of H or OH ions reveals a diminution during coagulation. 

 This can be readily explained on the basis of the amphoteric nature of the 

 protein. On the acid side of the isoelectric point the protein is an acid and 

 must possess some free COOH groupings. If these become neutralised, as 

 in anhydride formation, the acidity of the solution will be diminished. The 

 converse will hold true in alkaline solution where NH 2 groups function as 

 basic influences. 



The explanation of the primary reaction as simply involving an internal 

 dehydration seems most reasonable on account of the great number of ways 

 in which denaturation can be brought about. Light, heat, mechanical shock, 

 undue strain as in the surface of expanding air bubbles, or any marked 

 double phase such as is produced by the mixing of two immiscible liquids, 

 acidity, alcohol, all these agents bring about a change such that the protein 

 becomes insoluble. The action of alcohol is interesting in that in this reagent 

 we possess one which can bring about both changes, but that if conditions are 



